Molded panels of mineral-wool, fiberglass wool or plastic fibers heat cured in a thermosetting resin are well known in the art to be suitable for use as automobile headliners, door panels, and other automobile interior structures, as well as other structural panel applications in buildings, mobile homes, boats and the like. One common method of manufacturing such panels is to first contact a fibrous material with a water soluble thermosetting resin to form a resin impregnated mat. A panel of a desired contour may be readily formed from such a resin impregnated mat by placing the impregnated mat in a mold and subjecting the mat to temperature and pressure for a selected period of time sufficient to cure the resin and shape the mat into the desired panel contour.
Many thermosetting resin systems used in the prior art to wet mineral or glass fibers to form resin impregnated fibrous mats suitable for heat curing under pressure in a press or mold to provide a contoured panel have been urea formaldehyde, urea phenol formaldehyde, or urea phenolic based resins. When used in a closed environment, for example the interior of an automobile, panels produced from such urea based resin have been known to undesirably release an odor, as well as a residue containing phenols and formaldehyde, when exposed to high humidity and temperature conditions.
Melamine based resins have been suggested for use in resin impregnated fibrous mats for forming cured products. For example, a resin impregnated fibrous mat is disclosed in U.S. Pat. No. 3,953,632 wherein the mat is formed of randomly oriented plastic fibers that have been impregnated with a thermosetting resin and a thermoplastic copolymer. The thermosetting resin is selected from the group consisting of melamine-formaldehyde, hexamethoxymethyleneamine and urea-formaldehyde resins, and the thermoplastic copolymer is the product of the polymerization of a plurality of monomers at least one of which is a vinyl compound with an acid generating catalyst. After partially curing in a kiln or oven, the mat may be pressure shaped in a press or mold between opposing plates to produce a heat cured, pressed or mold sheet of a desired surface contour.
U.S. Pat. No. 4,960,826 discloses a binding adhesive useful in forming resin impregnated fibrous products, especially glass fiber containing products, such as pipe insulation, brake insulation, board products, and molded automotive products such as top liners and hood liners. The disclosed binding adhesive comprises an essentially aqueous res(ole)(ite)-melamine composition having an A-stage form containing residues of free melamine(s) to aldehydes(s) to phenolic compound(s) in a molar equivalent ratio ranging from about 0.2:1.5:1 to 0.8:3.5:1. The A-stage form of the res-melamine resin is said to be low temperature safe-storage stable and to be essentially infinitely soluble in water. It is further disclosed in U.S. Pat. No. 4,960,826, that a resinated glass fiber matrix may be readily formed by heat curing a resin impregnated glass wool at elevated temperatures. By application of heat to the resin impregnated glass wool in a press, mold or curing oven, the C-stage composition of the melamine-aldehyde-phenolic system is formed to provide a fiber reinforced resin product having outstanding resistance to punking or thermal attack and suitable hardness.
During the heat curing of melamine aldehyde composition, trimethylamines are formed as a reaction product. As trimethylamines carry a pungent fishy odor and may also be undesirable to breathe, it is desirable that panels formed using melamine based resins be manufactured in a manner that minimizes the release of aldehyde, phenolic and trimethylamine gases. Urea based resin panels which release significant levels of phenolic and/or aldehyde gases, or melamine based resins which release significant levels of phenolic, aldehyde and/or trimethylamine gases, may well be unsuitable for use in environments where people or animals will be exposed to such gas releases, for example closed environments such as home interior or vehicle occupant cabins.